Search results for "Proton"

showing 10 items of 5886 documents

Computational Modeling of Biological Systems: The LDH Story

2010

Lactate dehydrogenases, LDH, catalyzed reaction has been used in this chapter as a conductor wire to present the evolution and difficulties on computing methods to model chemical reactions in enzymes, since the early calculations based at semiempirical level carried out in gas phase to the recent sophisticated simulations based on hybrid Quantum Mechanical/Molecular Mechanics Dynamics (QM/MM MD) schemes. LDH catalyzes the reversible transformation of pyruvate into lactate. The chemical step consists in a hydride and a proton transfer from the cofactor (NADH) and a protonated histidine (His195), respectively. This fact has generated a lot of controversy about the timing of both transfers in …

biologyProtonChemistryHydridebiology.proteinActive siteThermodynamicsProtonationPotential of mean forceChemical reactionQuantumEnzyme catalysis
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Dehydrochlorination of Hexachlorocyclohexanes Catalyzed by the LinA Dehydrohalogenase. A QM/MM Study

2015

The elucidation of the catalytic role of LinA dehydrohalogenase in the degradation processes of hexachlorocyclohexane (HCH) isomers is extremely important to further studies on the bioremediation of HCH polluted areas. Herein, QM/MM free energy simulations are employed to provide the details of the dehydrochlorination reaction of two HCH isomers (γ and β). In particular, the role of the protonation state of one of the catalytic residues-His73-is explored. Based on our calculations, two distinct minimum free energy pathways (concerted and stepwise) were found for γ-HCH and β-HCH. The choice of the reaction channel for the dehydrochlorination reactions of γ- and β-HCH was shown to depend on t…

biologyProtonConcerted reactionStereochemistryHexachlorocyclohexaneActive siteProtonationSurfaces Coatings and FilmsCatalysisQM/MMchemistry.chemical_compoundchemistryComputational chemistryMaterials Chemistrybiology.proteinDegradation (geology)Physical and Theoretical ChemistryThe Journal of Physical Chemistry B
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Potential ATPase mimics by polyammonium macrocycles: Criteria for catalytic activity

1992

Abstract A series of polyammonium macrocycles, ranging in size from the 18-membered ring [18]aneN6 to the 36-membered [36]aneN12 were examined as potential ATPase mimics. The rates of hydrolysis of ATP were followed at pH 3.0 and 7.0 using 31P NMR and HPLC techniques. Stability constants as a function of degree of protonation, distribution curves for the ligands as a function of pH, and distribution curves for the mixed species of nucleotides, inorganic phosphate, and macrocycle were also determined. All of the macrocycles catalyzed the hydrolysis of ATP to some extent compared to noncatalyzed hydrolysis. A critical dependence on macrocyclic ring size was observed, with [21]aneN7 being the …

biologyStereochemistryATPaseOrganic ChemistryProtonationCrystal structureRing (chemistry)PhosphateBiochemistryRing sizeHydrolysisCrystallographychemistry.chemical_compoundchemistryATP hydrolysisDrug Discoverybiology.proteinMolecular BiologyBioorganic Chemistry
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Revision of the structure of torrentin

1989

Abstract The structure of the eudesmanolide torrentin from Artemisia herba-alba subs valentine has been revised on the basis of high-field 1 H NMR spectroscopy and chemical correlations.

biologyStereochemistryArtemisia herba-albaChemistryProton NMRPlant ScienceGeneral MedicineHorticulturebiology.organism_classificationMolecular BiologyBiochemistryPhytochemistry
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The C-12 and C-20 configurations of some neo-clerodane diterpenoids isolated from Teucrium species

1986

Abstract A convenient and conclusive method for determining the C-12 stereochemistry of neo-clerodan-20,12-olide derivatives, even when only one epimer is available, is by 1H NMR NOE measurements. The C-12 configuration of 26 neo-clerodane diterpenoids isolated from Teucrium species has been re-examined by using this type of experiment. The results indicated that all the previous assignments were correct, except for teupyreinin, where the previously assigned C-12(S) configuration must be amended to C-12(R). This was confirmed by chemical transformations and additional 1H and 13C NMR studies. Furthermore, the NOE experiments allowed the assignment of a C-20(S) configuration for teuflavin, th…

biologyStereochemistryPlant ScienceGeneral MedicineHorticultureCarbon-13 NMRbiology.organism_classificationBiochemistryTeucriumchemistry.chemical_compoundchemistryProton NMRMoleculeEpimerDiterpeneMolecular BiologyPhytochemistry
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Bis-urea macrocycles with a deep cavity.

2015

Two configurational isomers of bis-urea macrocycles have been synthesized, and their neutral molecule recognition was studied by X-ray crystallography and (1)H NMR experiments. Cooperative action between the deep cavity and the urea groups and the influence of dipole alignments on molecular recognition are discussed.

bis-urea macrocyclesChemistryStereochemistryMetals and AlloysStereoisomerismGeneral ChemistrychemistryCatalysisdeep cavitySurfaces Coatings and FilmsElectronic Optical and Magnetic MaterialsDipolechemistry.chemical_compoundMolecular recognitionComputational chemistryMaterials ChemistryCeramics and CompositesProton NMRUreata116molecule recognitionNeutral moleculeChemical communications (Cambridge, England)
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Proton-irradiated breast cells: molecular points of view

2019

Abstract Breast cancer (BC) is the most common cancer in women, highly heterogeneous at both the clinical and molecular level. Radiation therapy (RT) represents an efficient modality to treat localized tumor in BC care, although the choice of a unique treatment plan for all BC patients, including RT, may not be the best option. Technological advances in RT are evolving with the use of charged particle beams (i.e. protons) which, due to a more localized delivery of the radiation dose, reduce the dose administered to the heart compared with conventional RT. However, few data regarding proton-induced molecular changes are currently available. The aim of this study was to investigate and descri…

breast cancer cDNA microarray gene signature proton therapy radiation Breast Breast Neoplasms Cell Line Tumor DNA Complementary Dose-Response Relationship Radiation Female Gene Expression Profiling Gene Expression Regulation Neoplastic Humans Inflammation MCF-7 Cells Oligonucleotide Array Sequence Analysis Phenotype Proton Therapy Radiation Tolerance Radiotherapy ProtonsDNA ComplementaryHealth Toxicology and Mutagenesismedicine.medical_treatmentBreast NeoplasmsCell fate determinationRadiation Tolerancegene signature03 medical and health sciences0302 clinical medicineBreast cancerbreast cancerCell Line TumorRegular Papermedicineproton therapyHumansRadiology Nuclear Medicine and imagingBreastClonogenic assayBiologyProton therapyOligonucleotide Array Sequence Analysis030304 developmental biologyInflammationcDNA microarray0303 health sciencesRadiotherapyChemistryGene Expression ProfilingBreast cancer; radiation; cDNA microarray; gene signature; proton therapyCancerDose-Response Relationship RadiationGene signaturemedicine.diseaseGene Expression Regulation NeoplasticGene expression profilingRadiation therapyradiationPhenotype030220 oncology & carcinogenesisMCF-7 CellsCancer researchFemaleProtons
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Effect of buffer nature and concentration on the chromatographic performance of basic compounds in the absence and presence of 1-hexyl-3-methylimidaz…

2019

Abstract In reversed-phase liquid chromatography, the performance for basic compounds is affected by the interaction of the protonated (cationic) species with the anionic free silanols on the alkyl-bonded stationary phases. Using aqueous-organic mobile phases in the absence of additives, the retention may be too high, and the peaks be broad and asymmetric. The performance is improved by addition to the mobile phase of ionic liquids, from which 1-hexyl-3-methylimidazolium chloride ([C6MIm][Cl]) has especially good characteristics. A recent report has also revealed that the use of the phosphate system as buffer, at varying concentration and pH, may have a significant role in the chromatograph…

buffer systemsAcetonitrilesAdrenergic beta-AntagonistsIonic LiquidsProtonationBuffers010402 general chemistry01 natural sciencesBiochemistryChlorideAnalytical Chemistryionic liquidschemistry.chemical_compoundreversed-phase liquid chromatographyBoratesmedicineFormateβ-Adrenoceptor antagonistsChromatography High Pressure LiquidChromatography Reverse-PhaseChromatography010401 analytical chemistryOrganic ChemistryCationic polymerizationImidazolesWatersilanol effectGeneral MedicineReversed-phase chromatographyHydrogen-Ion ConcentrationPhosphate0104 chemical sciencesSilanolchemistryIonic liquidSolventsmedicine.drug
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Tear <sup>1</sup>H Nuclear Magnetic Resonance-Based Metabolomics Application to the Molecular Diagnosis of Aqueous Tear Deficiency and Me…

2020

<b><i>Purpose:</i></b> Meibomian gland dysfunction (MGD) is a major cause of signs and symptoms related to dry eyes (DE) and eyelid inflammation. We investigated the composition of human tears by metabolomic approaches in patients with aqueous tear deficiency and MGD. <b><i>Methods:</i></b> Participants in this prospective, case-control pilot study were split into patients with aqueous tear deficiency and MGD (DE-MGD [<i>n</i> = 15]) and healthy controls (CG; <i>n</i> = 20). Personal interviews, ocular surface disease index (OSDI), and ophthalmic examinations were performed. Reflex tears collected by capillarity were pr…

business.industryDry eyesMeibomian gland dysfunctionAqueous tear deficiencyGeneral Medicinemedicine.diseaseSensory Systems03 medical and health sciencesCellular and Molecular NeuroscienceOphthalmology0302 clinical medicineNuclear magnetic resonanceMetabolomicsmedicine.anatomical_structure030221 ophthalmology & optometrymedicineProton NMRTearsOcular Surface Disease Indexsense organsEyelidbusiness030217 neurology & neurosurgeryOphthalmic Research
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Calculated organ doses using Monte Carlo simulations in a reference male phantom undergoing HDR brachytherapy applied to localized prostate carcinoma

2013

Purpose : The aim of this study was to obtain equivalent doses in radiosensitive organs (aside from the bladder and rectum) when applying high-dose-rate (HDR) brachytherapy to a localized prostate carcinoma using60Co or 192 Ir sources. These data are compared with results in a water phantom and with expected values in an infinite water medium. A comparison with reported values from proton therapy and intensity-modulated radiation therapy (IMRT) is also provided. Methods : Monte Carlo simulations in Geant4 were performed using a voxelized phantom described in International Commission on Radiological Protection (ICRP) Publication 110, which reproduces masses and shapes from an adult reference…

business.industryEquivalent dosemedicine.medical_treatmentBrachytherapyGeneral MedicineEffective dose (radiation)Imaging phantomRadiation therapyAbsorbed doseMedicineDosimetrybusinessNuclear medicineProton therapyMedical Physics
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